A 1300 nm band zero dispersion single mode fiber network is well known as a fiber network of an optical transmission system. This fiber network is able to obtain almost zero dispersion transmissions at a receiving end by transmitting optical signals of a 1300 nm wavelength.
Recently, optical transmissions have been attempted at a wavelength band of around 1550 nm, which is an excitation band of an erbium doped fiber amplifier (EDFA). The EDFA was disposed in an optical transmission path, using an existing 1300 nm band zero dispersion single mode fiber network. Furthermore, many trials have been taken into consideration, wherein wavelength division multiplex transmissions are carried out at wide wavelength bands of around 1550 nm, aiming at a further high bit-rate transmission.
Single mode fiber in an existing 1300 nm band zero dispersion single mode fiber network has positive dispersion values and positive dispersion slope characteristics in which the dispersion quantity becomes large in accordance with an increase in wavelength. Therefore, in the instance where a wavelength division multiplex transmission is performed at a 1550 nm wavelength band using an existing zero dispersion 1300 nm single mode fiber network, the dispersion quantity is increases in line with an increase of the transmission distance of single mode fibers. Accordingly, the separation of multiplex-transmitted signals of each wavelength will be difficult, thereby causing a problem to arise in reliability of the wavelength division multiplex transmissions. Therefore, wavelength division multiplex transmissions have usually been attempted, using a communication link (transmission link) in which a dispersion compensating fiber having a large negative dispersion value and negative dispersion slope characteristics is connected to a single mode fiber.